In the prior art, there are known data storage systems such as e.g. described in connection with FIG. 1A below, in which multiple client computers are connected via a communication network with one or more file server systems managing one or more file systems for I/O access by the client computers. At certain times, it may be desirable to exchange the one or more (legacy) file servers with new file servers in order to improve performance of the whole data storage system, e.g., because the newer file servers may be adapted to manage more file systems or larger file systems (including enabling more data storage space and/or larger number of file system objects), enable more efficient input/output (I/O) performance, enable use of larger storage units or storage units containing more efficient storage device technologies.
Still, it may be desirable to keep the already existing file system(s) including file system structure (such as an existing file tree structure) and user data (file content) thereof, while it is, in principle, desirable to enable the users to access the existing file system(s) without interruption or at least with only a single interruption that is as short as possible. An example of an apparatus and a method for a hard-ware based file system is described in U.S. Pat. No. 7,457,822 B1, which is herein incorporated by reference.